如何从android studio项目中的JsonObject提取数据

我正在android studio中开发RESTAPI应用程序。我想从一个JsonObject中提取数据，在使用翻新库检索数据时，我使用模型类保存了这个JsonObject。但它显示了以下错误

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.covid_19updates, PID: 15236
    java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
     Caused by: java.lang.reflect.InvocationTargetException
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 
     Caused by: org.json.JSONException: No value for flag
        at org.json.JSONObject.get(JSONObject.java:400)
        at org.json.JSONObject.getJSONObject(JSONObject.java:620)
        at com.example.covid_19updates.MainActivity$onCreate$1.onResponse(MainActivity.kt:52)
        at retrofit2.DefaultCallAdapterFactory$ExecutorCallbackCall$1.lambda$onResponse$0$DefaultCallAdapterFactory$ExecutorCallbackCall$1(DefaultCallAdapterFactory.java:89)
        at retrofit2.-$$Lambda$DefaultCallAdapterFactory$ExecutorCallbackCall$1$hVGjmafRi6VitDIrPNdoFizVAdk.run(Unknown Source:6)
        at android.os.Handler.handleCallback(Handler.java:938)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:223)
        at android.app.ActivityThread.main(ActivityThread.java:7656)
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 

我提取的单个数据对象如下所示：

{"updated":1606563124609,"country":"Afghanistan","countryInfo":{"_id":4,"iso2":"AF","iso3":"AFG","lat":33,"long":65,"flag":"https://disease.sh/assets/img/flags/af.png"},"cases":45966,"todayCases":127,"deaths":1752,"todayDeaths":12,"recovered":36709,"todayRecovered":414,"active":7505,"critical":93,"casesPerOneMillion":1170,"deathsPerOneMillion":45,"tests":146413,"testsPerOneMillion":3727,"population":39280785,"continent":"Asia","oneCasePerPeople":855,"oneDeathPerPeople":22421,"oneTestPerPeople":268,"activePerOneMillion":191.06,"recoveredPerOneMillion":934.53,"criticalPerOneMillion":2.37}

我想检索countryInfo对象中的数据。下面是我的模态类

data class Covid(
    var updated: Long,
    var country:String,
    var countryInfo:JSONObject,
    var cases:Int,
    var todayCases:Int,
    var deaths:Int,
    var todayDeaths:Int,
    var recovered:Int,
    var todayRecovered:Int,
    var active:Int,
    var critical:Int,
    var casesPerOneMillion:Double,
    var deathsPerOneMillion:Double,
    var test:Long,
    var testPerOneMillion:Double,
    var population:Long,
    var continent:String,
    var oneCasePerPeople:Double,
    var oneDeathPerPeople:Double,
    var oneTestPerPeople:Double,
    var activePerOneMillion:Double,
    var recoveredPerOneMilion:Double,
    var criticalPerOneMillion:Double
)

还有我为获取数据而编写的代码

override fun onResponse(call: Call<List<Covid>>, response: Response<List<Covid>>) {
                var list = response.body()
                Log.d("Response: ",response.toString())
                var countryList = ArrayList<String>()
                var countList = ArrayList<String>()
                var activeList = ArrayList<String>()
                var deathList = ArrayList<String>()
                var recoveredList = ArrayList<String>()
                var imageList = ArrayList<String>()
                list?.map { item ->
                    countryList.add(item.country.toString())
                    var totalCases = "Total Cases: "+item.cases.toString()
                    var activeCases = "Active Cases: "+item.active.toString()
                    var deaths = "Total Deaths: "+item.deaths.toString()
                    var recovered = "Total Recovered: "+item.recovered.toString()
                    var image = item.countryInfo.getJSONObject("flag").toString()
                    countList.add(totalCases)
                    activeList.add(activeCases)
                    deathList.add(deaths)
                    recoveredList.add(recovered)

                }

override-fun-onResponse（调用：调用，响应：响应）{
var list=response.body（）
Log.d（“Response:，Response.toString（））
var countryList=ArrayList（）
var countList=ArrayList（）
var activeList=ArrayList（）
var deathList=ArrayList（）
var recoveredList=ArrayList（）
var imageList=ArrayList（）
列表？.map{item->
countryList.add（item.country.toString（））
var totalCases=“Total Cases:+item.Cases.toString（）
var activeCases=“Active Cases:+item.Active.toString（）
var deathes=“死亡总数：”+item.deathes.toString（）
var recovered=“总回收量：”+item.recovered.toString（）
var image=item.countryInfo.getJSONObject（“标志”）.toString（）
countList.add（totalCases）
添加（activeCases）
死亡运动员。添加（死亡）
recoveredList.add（已恢复）
}

尝试为CountryInfo创建一个单独的数据类

新冠病毒

val countryInfo: CountryInfo,

然后

旁注，您可以使用从JSON自动生成kotlin对象

    data class CountryInfo(
val _id: Int,
val iso2: String,
val iso3: String,
val lat: Double, //trust me you should use double on latLng values. 
val long: Double,
val flag: String

)